1. Field of the Invention
The present invention relates to a bearing for supporting a rotated shaft, and particularly to a self-lubricating composite bearing that automatically supplies lubricating media with different viscosities to form a smoothening tribology interface around the periphery of the rotated shaft even under a variety of severe operating conditions.
2. Description of the Related Art
To avoid friction-induced constraints between shaft and bearing, a lubricating medium is generally applied to form a smoothening tribology interface around the periphery of the rotated shaft being supported in the bearing. However, it is inconvenient and laborious to regularly apply the lubricant to a bearing. In case the lubricating medium is not supplied in time, friction-induced heat will be generated causing insufficient lubrication and rapidly damage. To mitigate this problem, self-lubricating bearings are created. The lubricating media can be classified as lower viscosity lubricating oil and higher viscosity lubricant (including but not limited to such as grease, hybrid lubrication agent containing solid lubricating grains). Conventional self-lubricating bearings commonly use the lubricating oil for forming a tribology interface between the axial hole of the bearing and the periphery of the rotated shaft being supported in the bearing. However, the tribology interface formed by the lubricating oil has a thin thickness, limiting the side-load capacity of the bearing. Further, the higher the temperature, the lower is the viscosity of the lubricating oil, causing the tribology interface to be thinner. If the shaft is continuously rotated at a high speed and with a thinning tribology interface, the lubricating oil may be forced away from the axial hole of the bearing, causing the shaft being directly worn out or even collided with the bearing. Under such a condition, the friction-induced heat and noise will speed up the bearing damage.
On the contrary, the grease has a viscosity higher than that of the lubricating oil, forming a relatively thicker tribology interface within a bearing around the periphery of the shaft and enhancing the loading capacity of the bearing. Because of the characteristic of high viscosity, grease is commonly used in ball bearings. However, conventional ball bearing comprises many long and thin components. As compared with the self-lubricating bearing, conventional ball bearing has the drawbacks of high cost, noisy, complicated structure and weaker structural strength. When a ball bearing is applied to high temperature, high subzero temperature, high load and high speed conditions, the loading capacity, resistance against high- and low-temperature and lifespan of the ball bearing will confront a critical challenge. As compared with the ball bearing, the self-lubricating bearing has the advantages of low cost, quiet, simple structure and higher structural strength. Nevertheless, self-lubricating bearing is usually made from a porous material that is not practical for impregnating with lubricant such as grease or hybrid lubrication agent containing solid lubricating grains for forming an evenly distributed tribology interface due to poor mobility in the pores. The mobility is getting worse under a low operational temperature condition. Directly applying lubricant to the inner wall of a self-lubricating bearing for supporting a shaft in the bearing can temporarily enhance the loading capacity, however friction-induced temperature rise problems will occur soon after consuming of the applied lubricant for a high speed rotation of the shaft.
Accordingly, it is desirable to provide a self-lubricating composite bearing that continuously supplies lubricating medium to form an evenly distributed tribology interface in between the shaft and bearing when applied to abnormal high- and low-temperatures, high load and high speed conditions.